This invention relates to the noninvasive measurement of parameters such as blood pressure, heart and respiratory rate and oxygen saturation in man and animals, and more particularly to the optical noninvasive measurement of blood parameters.
A number of noninvasive methods of measuring blood parameters are known. For example, blood pressure has been measured by the auscultatory method which uses a cuff and a stethoscope or microphone, and by the oscillometric method which only requires a cuff applied to a body member. The conventional oscillometric method relies on the small-amplitude pulsatile pressure oscillations communicated to the cuff by the underlying artery in the body member during cuff deflation from above systolic pressure to zero pressure. Such arterial pressure oscillations cause corresponding oscillations in cuff pressure which can be amplified and used to identify systolic, mean and diastolic pressure. For example, it has been established by Posey et al. that the cuff pressure for maximal amplitude oscillations corresponds to mean arterial pressure. See Posey et al., “The Meaning of the Point of Maximum Oscillations in Cuff Pressure in the Direct Measurement of Blood Pressure,” Part 1, Cardiovascular Res. Ctr. Bull. 8(1):15–25, 1969. See also Ramsey, “Noninvasive Automatic Determination of Mean Arterial Pressure,” Med. Biol. Eng. Comput. 17:17–18, 1979; and Geddes et al., “Characterization of the Oscillometric Method for Measuring Indirect Blood Pressure,” Annals of Biomedical Engineering, Vol. 10, pp. 271–280, 1982. All such references are incorporated herein by reference.
Commercially available oscillometric devices are useful for some applications but are not particularly suited for use on a subject's forehead, for example. A need exists for improvements in vital sign monitors to enable reliable monitoring with noninvasive sensor units which can be quickly applied to a subject during and after cardiopulmonary resuscitation (CPR), during transport, or during surgery or other procedures in conscious and anesthetized subjects.